1. Field of the Invention
The present invention relates to a method and apparatus for infrared gas analysis.
2. Background Art
In an apparatus for infrared gas analysis, a dehumidifier 83 such as an electronic cooling device, as shown in FIG. 10, has been heretofore provided in a feed line 82 of a sample gas SG for a gas analysis section 81 to dehumidify the sample gas SG and to feed the dehumidified sample gas SG to the gas analysis section 81 since a necessity exists for suppressing an influence of water included in the sample gas to the lowest level possible, when measurement is performed of a concentration of a specific component to be measured (a gas to be measured) that is included in the sample gas.
In a prior art method, however, not only was a construction of the entire measurement system more complex due to installment of the dehumidifier 83 therein, but hardship was also encountered in measurement of a gas with a high solubility in water. Furthermore, in the above construction, since measurement is performed after removal of water in the sample gas SG, a concentration of a component to be measured in the sample gas SG is raised by a value corresponding to a partial pressure of the water; therefore, a necessity arises for a correction with respect to a water partial pressure after the measurement.
In this case, as shown in FIG. 10, there arise requirements that a flow path 84 is connected to the sample gas line 82 so as to be branched therefrom upstream of the dehumidifier 83 of the sample gas line 82 and a water concentration meter 85 is provided in the branch flow path 84 to measure a water concentration included in the sample gas before dehumidification, or alternatively, that if no water concentration meter 85 is provided, a water concentration is estimated.
Even though a correction with respect to a water partial pressure is performed as described above, however, a correct concentration of a component to be measured has always been unable to achieve.
Meanwhile, in recent years, a problem of control on gas exhausted from an engine of a vehicle such as an automobile in running has increasingly drawn great attention and an importance has increased of grasping a quantity and concentration of the exhaust gas with certainty in order to preserve or protect the global environment. In a case where the dehumidifier 83 is installed as described above, however, since the entire measurement system becomes bulky, a great difficulty arises in mounting the apparatus for infrared gas analysis in a vehicle with a limited space available therein and the installment of a dehumidifier 83 itself results in cost up of the measurement system as a whole.